Radioisotopes have significant utility for a wide range of medical applications. For example, technetium-99m is a primary radioisotope employed in diagnostic nuclear medicine. The importance of technetium-99m to clinical procedures is highlighted by the fact that more than 13 million diagnostic procedures using technetium-99m are performed each year in the United States alone.
Technetium-99m has a combination of desirable physical properties, including its gamma decay mode and energy, that are ideally suited for single photon emission computed tomography. Moreover, technetium's chemical reactivity and versatility allow it to be conveniently complexed to carrier or targeting agents, such as antibodies, peptides, and other molecules, which allows particular tissues to be selectively imaged or scanned. Because technetium-99m has a short half-life (t1/2=6 h), this radioisotope, when used in clinical practice, is typically produced from its longer-lived parent nuclide, molybdenum-99 (t1/2=66 h) using a chromatographic column generator. For an example of a molybdenum-99/technetium-99m generator, see U.S. Pat. No. 5,774,782 to Mirzadeh et al. Removing the technetium-99m daughter nuclide from the generator (i.e., separating it from molybdenum) is typically performed by “milking” the generator a few times daily by pulling normal saline through the column to elute the soluble technetium-99m for complexation in “kits” for subsequent patient injection.
Commercial quantities of molybdenum-99 have been produced in nuclear reactors over the years through the uranium fission process (for example, see U.S. Pat. No. 3,799,883 to Arino et al.) utilizing highly enriched uranium-235 that requires extensive security and non-proliferation safeguards. Unfortunately, the fission process, whether it is based on low or high enriched uranium, yields only a small amount of molybdenum-99 with a large array of undesirable fission products that present significant infrastructure, health and security, liability, handling, storage, and waste issues and associated costs. Further, this mode of production requires dedicated and reliable nuclear reactors, support facilities and operation thereof to maintain a continuous supply. The United States currently depends solely on a limited number of foreign suppliers of molybdenum-99.